Polyester-polyurethane hybrid resins are well-known in the art of thermoset molding compositions. These resins are normally tougher than polyesters and stronger, stiffer and have greater thermal resistance than polyurethanes. Such hybrid resins usually comprise a hydroxy-terminated unsaturated polyester polyol, an ethylenically unsaturated monomer such as styrene, a polyisocyanate, a free radical polymerization initiator and often other additives. They can be easily adapted to many common thermoset molding techniques employed in polyurethane and unsaturated polyester industries. Such hybrid resins are commercially available from Amoco Chemical Company under the trademark Xycon and are supplied as two component liquid systems. One component, the A-side, contains the polyisocyanate and the free radical polymerization initiator, while the other component, the B-side, contains the hydroxy-terminated unsaturated polyester polyol/styrene solution and optionally a polyurethane catalyst and/or filler.
There are many end uses for polyester-polyurethane hybrid resin compositions including the manufacture of parts for and construction of automobiles, trucks, boats, machine housings and household items such as bath fixtures. In many of these applications, it is desirable to provide resins which have flame retardant properties. However, one problem associated with the manufacture of polyester-polyurethane hybrid resins having flame retardancy is the loss of desirable properties such as strength, stiffness and thermal resistance due to the addition of flame retardant compounds. Another problem is the settling out of the flame retardant compound from the hybrid resin composition. Still another problem is the effect which the flame retardant compound may have on moldability of the hybrid resin.
The general object of this invention is to provide polyester-polyurethane hybrid resin compositions having flame retardant properties without having an adverse effect on other physical properties of the hybrid resin compositions. It is another object to provide a simple, inexpensive method for making such flame retardant polyester-polyurethane hybrid resin compositions. It is yet another object to provide molded articles having improved flame retardancy which are made from the hybrid resins. Other objects appear hereinafter.
These and other objects are achieved by polyester-polyurethane hybrid resin compositions which are formed by the reaction of an A-side composition and a B-side composition. The A-side composition comprises a polyfunctional isocyanate compound and a free radical polymerization initiator. The B-side composition comprises a mixture of an ethylenically unsaturated monomer solution which has dissolved therein about 40-90 wt. % of a substantially water-free, hydroxyl-terminated, unsaturated polyester polyol having an acid number less than five, said polyester polyol comprising an oligomer obtained by the condensation reaction of a polycarboxylic acid and an unsaturated polycarboxylic acid or anhydride with a polyhydric alcohol, wherein the polycarboxylic acid moieties of the polyester polyol comprise from about 15 to about 50 mole % of at least one halogenated aromatic polycarboxylic acid. Unexpectedly, it has been found that by using polyols comprising halogenated aromatic polycarboxylic acids, flame retardant properties can be achieved without adversely affecting other properties of the hybrid resins. These halogenated aromatic polycarboxylic acids can be substituted for all or part of conventional polycarboxylic acids such as isophthalic acid in a hybrid resin formulation without significantly affecting the preparation, processing, and basic engineering properties of the hybrid resin. This behavior is in contrast to the incorporation of other halogenated monomers in a hybrid resin formulation such as halogenated phthalic anhydrides or halogenated glycols which prevent the formation of hydroxyl-terminated unsaturated polyesters. The use of halogenated aromatic polycarboxylic acids in a flame retardant hybrid resin is also advantageous over adding conventional flame retardant additives because conventional additives impart flame retardance at the expense of other properties, such as gel time, flexural modulus and impact resistance.
For the purpose of this invention, the term "cure" or "curing" means the transformation of the polyester-polyurethane hybrid resin composition from a liquid or flowable paste to a solid cross-linked material at the time of molding. This curing occurs by cross-linking of the reactive sites in the hybrid resin system, including the reaction of the isocyanate with the reactive end groups of the polyol, and via the vinyl addition reaction between the ethylenically unsaturated monomer and the unsaturated polyester polyol. Depending on the catalyst employed, curing can optimally occur at temperatures of about 30.degree. C. to about 100.degree. C. for a time of between about one minute and about one hour. The term "polyfunctional" and the prefix "poly-" as used herein, are intended to include functionalities of two or greater.